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timers/nohz: Update NOHZ load in remote tick

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The way loadavg is tracked during nohz only pays attention to the load
upon entering nohz.  This can be particularly noticeable if full nohz is
entered while non-idle, and then the cpu goes idle and stays that way for
a long time.

Use the remote tick to ensure that full nohz cpus report their deltas
within a reasonable time.

[ swood: Added changelog and removed recheck of stopped tick. ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Scott Wood <swood@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/1578736419-14628-3-git-send-email-swood@redhat.com
This commit is contained in:
Peter Zijlstra (Intel) 2020-01-11 04:53:39 -05:00 committed by Ingo Molnar
parent 488603b815
commit ebc0f83c78
3 changed files with 28 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/sched/nohz.h
View File

@ -15,9 +15,11 @@ static inline void nohz_balance_enter_idle(int cpu) { }
#ifdef CONFIG_NO_HZ_COMMON
void calc_load_nohz_start(void);
void calc_load_nohz_remote(struct rq *rq);
void calc_load_nohz_stop(void);
#else
static inline void calc_load_nohz_start(void) { }
static inline void calc_load_nohz_remote(struct rq *rq) { }
static inline void calc_load_nohz_stop(void) { }
#endif /* CONFIG_NO_HZ_COMMON */

4
kernel/sched/core.c
View File

@ -3677,6 +3677,7 @@ static void sched_tick_remote(struct work_struct *work)
if (cpu_is_offline(cpu))
goto out_unlock;
curr = rq->curr;
update_rq_clock(rq);
if (!is_idle_task(curr)) {
@ -3689,10 +3690,11 @@ static void sched_tick_remote(struct work_struct *work)
}
curr->sched_class->task_tick(rq, curr, 0);
calc_load_nohz_remote(rq);
out_unlock:
rq_unlock_irq(rq, &rf);
out_requeue:
/*
* Run the remote tick once per second (1Hz). This arbitrary
* frequency is large enough to avoid overload but short enough

33
kernel/sched/loadavg.c
View File

@ -231,16 +231,11 @@ static inline int calc_load_read_idx(void)
return calc_load_idx & 1;
}
void calc_load_nohz_start(void)
static void calc_load_nohz_fold(struct rq *rq)
{
struct rq *this_rq = this_rq();
long delta;
/*
* We're going into NO_HZ mode, if there's any pending delta, fold it
* into the pending NO_HZ delta.
*/
delta = calc_load_fold_active(this_rq, 0);
delta = calc_load_fold_active(rq, 0);
if (delta) {
int idx = calc_load_write_idx();
@ -248,6 +243,24 @@ void calc_load_nohz_start(void)
}
}
void calc_load_nohz_start(void)
{
/*
* We're going into NO_HZ mode, if there's any pending delta, fold it
* into the pending NO_HZ delta.
*/
calc_load_nohz_fold(this_rq());
}
/*
* Keep track of the load for NOHZ_FULL, must be called between
* calc_load_nohz_{start,stop}().
*/
void calc_load_nohz_remote(struct rq *rq)
{
calc_load_nohz_fold(rq);
}
void calc_load_nohz_stop(void)
{
struct rq *this_rq = this_rq();
@ -268,7 +281,7 @@ void calc_load_nohz_stop(void)
this_rq->calc_load_update += LOAD_FREQ;
}
static long calc_load_nohz_fold(void)
static long calc_load_nohz_read(void)
{
int idx = calc_load_read_idx();
long delta = 0;
@ -323,7 +336,7 @@ static void calc_global_nohz(void)
}
#else /* !CONFIG_NO_HZ_COMMON */
static inline long calc_load_nohz_fold(void) { return 0; }
static inline long calc_load_nohz_read(void) { return 0; }
static inline void calc_global_nohz(void) { }
#endif /* CONFIG_NO_HZ_COMMON */
@ -346,7 +359,7 @@ void calc_global_load(unsigned long ticks)
/*
* Fold the 'old' NO_HZ-delta to include all NO_HZ CPUs.
*/
delta = calc_load_nohz_fold();
delta = calc_load_nohz_read();
if (delta)
atomic_long_add(delta, &calc_load_tasks);